. >> translator: he said look, fresh meat from el salvador. >> forced to work under threat of death in america's booming sex industry. >> these are slaves, but it's the most egregious kind of slavery, it's sex slaves. >> it's a billion dollar industry thriving in the heart of our cities. >> it's living quarters. >> how many people do you think live back here? >> i would say about four or five of them. >> where young women and girls find themselves trapped with no way out. >> this is a multi-billion dollar industry. >> msnbc goes undercover to investigate "sex slaves in america." >>> hello, i'm meredith vieira. every year human rights advocates estimate almost a million women worldwide are illegally bought and sold into sexual slavery. what you might not know is that over 17,000 of them end up right here in the united states. in the next hour, you will hear some of their harrowing stories. to protect these women, their names have been changed. it's a story that begins in the ruins of the shattered soviet empire and ends in heartland america. >> i was watching a lot of tv shows about hum